This invention relates generally to gas turbine engines and more particularly to a fuel nozzle for supplying fuel to the combustor of such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and burned for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In combustors used with aircraft engines, the fuel is supplied to the combustor through fuel nozzles positioned at one end of the combustion zone. A fuel nozzle typically includes a spray tip for precisely spraying fuel into a surrounding assembly, known as a swirler. The swirler also receives compressed air from the compressor and imparts a swirling motion to the air, thereby thoroughly mixing the fuel and air for combustion.
Because the fuel nozzle is located in the compressor discharge gas stream, it is exposed to relatively high temperatures. The presence of high temperatures around the fuel nozzle can cause the fuel passing through the nozzle fuel tube to form granules of carbon on the inner walls thereof. The carbon or coke formation in the fuel tube may cause the fuel nozzle to become clogged. Excessive temperatures can also cause the fuel in the fuel nozzle to gum up, thereby further causing the fuel nozzle to become clogged. In addition, if the fuel becomes overheated, it may begin to vaporize in the inner passageway, thereby resulting in intermittent or non-continuous fuel delivery to the combustor.
Consequently, conventional fuel nozzles typically include a heat shield in the form of a tubular housing that surrounds the fuel tube and spray tip so as to define an annular air gap therebetween. The air gap, or nozzle cavity, serves as a thermal barrier to protect the fuel in the fuel tube against coking.
During engine operation, the temperature of the housing is greater than the temperature of the fuel tube resulting in differential thermal expansion. This differential growth can cause the spray tip to be axially displaced from its proper positioning with respect to the housing. Operational risks such as nozzle cavity over-pressurization and carbon jacking (i.e., the build-up of hard carbon on nozzle internal surfaces) can also lead to axial displacement of the spray tip relative to the housing.
Such axial displacement can cause variations of the fuel spray impingement location in the swirler, which could impair the combustor exit temperature profile, engine emissions and engine start capability. Spray tip misalignment can also reduce the service life of the fuel nozzle, as well as the combustor, thereby increasing repair and maintenance costs. One known approach to preventing axial displacement is to use mechanical stops in the spray tip region to prevent axial motion of the spray tip in the aft direction. However, this approach does not address axial movement in the forward direction, which can also produce the above-mentioned problems.
Accordingly, there is a need for a fuel nozzle that maintains the proper axial positioning of the spray tip relative to the housing in both the forward and aft directions.
The above-mentioned need is met by the present invention which provides a fuel nozzle having a spray tip and a housing coaxially disposed around the spray tip. The fuel nozzle further includes a means for constraining bi-directional axial movement of the spray tip relative to the housing. The means for constraining bi-directional axial movement of the spray tip preferably includes first and second tabs formed on one of the housing and the spray tip and a third tab formed on the other one of the housing and the spray tip. The third tab is disposed between the first and second tabs to constrain bi-directional axial movement.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.